1. Field of the Invention
The present invention relates to a cooling apparatus for liquid-cooled internal combustion engine, and it is preferably applicable to an internal combustion engine of a vehicle.
2. Description of Related Art
As disclosed in JP-A-8-128559, it is known to maintain the cooling water temperature under light engine load higher than that under heavy engine load in order to improve the fuel consumption performance of a liquid-cooled internal combustion engine (hereinafter referred to as the "engine").
Since a circulating pump for circulating the cooling water is generally driven by the engine, the circulation flow rate of the cooling water which circulates through the engine varies in proportion to the engine speed as shown in FIG. 9. On the other hand, the cooling water temperature increases according to a decrease of the circulation flow rate. Accordingly, the circulation flow rate can be reduced by reducing the pump rotation speed when the engine load is light, because the cooling water temperature can be increased when the engine load is light.
According to the pump driven by the engine, the pump work is allowed to be small by reducing the circulation flow rate when the engine load is light. However, since the circulation flow rate is not variable according to the engine load, unnecessary pump work increases.